1. Field of the Invention
The present invention relates to electrophotographic photoconductors. More particularly, it relates to an electrophotographic photoconductor having a conductive support and a photosensitive layer formed thereon, the photosensitive layer containing a bis-enamine compound.
2. Description of the Prior Art
Conventional photosentive layers are utilized inorganic compounds such as selenium, cadmium sulfide, amorphous silicon and zinc oxide. In addition, many studies have been conducted for using organic photoconductive materials as electrophotographic photoconductors.
Basic properties required for electrophotographic photoconductors include the following properties.
(1) A high electrostatic chargeability of electric charge by corona discharge in dark place,
(2) Few reduction in electric charge in dark place by corona charge thus obtained,
(3) A quick dissipation of an electric charge by light irradiation,
(4) Few residual electric charge after light irradiation,
(5) A small rise in the residual potential and few reduction in the initial potential through the repetitive use and
(6) Few change in the electrophotographic properties and small decrease in the initial potential through repetitive use.
Conventional inorganic materials for electrophotographic photoconductors such as selenium and cadmium sulfide satisfy the above mentioned requirements as a photoconductor in terms of basic properties. However, such materials have drawbacks in the manufacturing process such as, for example, a strong toxicity, difficulty in forming films, little plasticity and a high manufacturing cost. In view of the future prospect, organic materials are more desired than inorganic ones for photoconductors seeing that inorganic materials are restricted in production owing to the depletion of natural resources, and are more likely to cause pollution because of the toxicity thereof.
In view of the above, a brisk research has been performed in recent years on electrophotographic photoconductors formed of organic materials. As a consequence, electrophotographic photoconductors using various organic materials are proposed and some of them are actually manufactured as a product.
Generally speaking, organic materials have several advantages over inorganic materials in that organic materials are more excellent in transparency, lighter in weight, easier to be formed into films than inorganic materials, and that organic materials have both positive and negative chargeability. Such advantages allow easy manufacture of photoconductors formed of organic materials.
Typical organic electrophotographic photoconductors so far proposed include a polyvinylcarbazole and its derivatives. These materials are not sufficient in film-forming properties, plasticity, solubility and adhesiveness. Although a certain degree of improvement has been made to give a photoconductor formed of a polyvinylcarbazole photosensitized with a pyrylium dye (as disclosed in Japanese Patent Publication No. SHO. 48(1973)-25658), and of a polyvinylcarbazole photosensitized with 2,4,7-trinitrofluorenone (as disclosed in U.S. Pat. No. 3,484,237). However, it is still desired to find a photoconductor which satisfies the above-mentioned basic properties as well as mechanical strength and high durability.
In recent years, as disclosed in U.S. Pat. No. 3,791,826, a function-distributed photoconductor is actively proposed wherein two different compounds performs two functions of photoconductive materials such as generation of carriers and transfer of generated carriers. Most of such carrier transferring materials in function-distributed photoconductors are organic compounds having a low molecular weight. Only a limited number of such compounds selected from a wide range thereof can satisfy the basic requirements of photoconductors.
In addition, Japanese Laid-Open Patent No. HEI 1(1989)-195455 discloses that use of a styrene compound containing an enamine group as a carrier transferring material has actualized development of an electrophotographic photoconductor with a considerable sensitivity. Japanese Laid-Open Patent No. HEI 1(1989)-195455 discloses a photoconductor having a conductive substrate and a photosensitive layer formed thereon, the photosensitive layer containing an enamine compound of the general formula (A): ##STR2## (wherein R.sup.1 is a hydrogen, an alkyl group, an alkoxy group, an aralkyl group, a di-substituted amino group, or an aryl group; R.sup.2 is hydrogen, an alkyl group, an aryl group that may have a substituent, a condensed polycyclic ring; Ar.sub.1, Ar.sub.2, and Ar.sub.3 represent an alkyl group, an aryl group, a condensed polycyclic group or a heterocyclic group).
However, the above compounds a poor solubility, because they have a high melting point. Coating them will deposit a crystal. Even such compounds having a low melting point did not provide a photoconductor with sufficient properties just because of their inferior sensitivity and the like.